1. Field of the Invention
The present invention relates to a film-forming composition, and more precisely to a composition for forming an insulating material such as an insulating film having good film properties in point of the dielectric constant and the mechanical strength thereof, to an insulating film formed from the composition, and to an electronic device having the insulating film.
2. Description of the Related Art
In recent years, accompanied by the progress of high integration, multifunction and high performance in the field of electronic materials, circuit resistance and condenser capacity between wirings have been increased thus causing increase of electric power consumption and delay time. Particularly, increase of delay time becomes a large factor for the reduction of signal speed of devices and generation of crosstalk, so that reduction of parasitic resistance and parasitic capacity are in demand for the purpose of attaining acceleration of devices by reducing this delay time. As one of the concrete measures for reducing this parasitic capacity, an attempt has been made to cover periphery of wiring with a low dielectric layer insulating film. Also, the layer insulating film is expected to have superior heat resistance which can withstand the thin film formation step at the time of mounting substrate production and chip connection, pin attachment and the like post steps and also chemical resistance that can withstand wet process. In addition, a low resistance Cu wiring has been introduced in recent years instead of the Al wiring, and accompanied by this, flattening by CMP (chemical mechanical polishing) is commonly carried out, so that high mechanical strength which can withstand this process is in demand.
Polybenzoxazole and polyimide are widely known for insulating films of good heat resistance. However, since they contain a nitrogen atom of low polarity, they could not form films that are satisfactory in point of the necessary low level of dielectric constant, the water absorption resistance, the durability and the hydrolysis resistance.
In general, many organic polymers are poorly soluble in organic solvent, and a technique of preventing polymer deposition in coating solutions and preventing depositions in insulating films is an important theme in the art. To solve the problems, when the polymers are so modified that their main chain has a folded structure in order to have an increased solubility, then their glass transition point lowers and their heat resistance also lowers, and, after all, it is not easy to obtain polymers that satisfy both the intended properties and the solubility.
For an insulating film, a highly heat-resistant resin having a backbone structure (main chain) of polyarylene ether (JP-T 2002-530505 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application), U.S. Pat. Nos. 6,380,347, 5,965,679 and JP-T 2002-534546) is related, but it is desired to further lower the dielectric constant of the resin for realizing high-speed devices. A method has been tried, which comprises making a film porous for lowering the dielectric constant of the resulting porous film. However, it is desired to lower the dielectric constant of the film while the porosity of the film is kept low in order to keep the film properties. It is also desired not to make a film porous but to make the film have a bulk specific dielectric constant of 2.6 or less, more preferably 2.5 or less.
JP-T 2004-504455 discloses a diamantane monomer substituted with an aryl group and a carbon-carbon triple bond. However, the film formed from the monomer could not have the desired specific dielectric constant of 2.5 or less, since the ratio of the benzene ring having a large electronic polarization in the compound is high.
In general, an organic polymer is poorly adhesive to silicon wafers, and is therefore often problematic in point of film peeling during wiring.
A related art, dual-damascene interconnection structure has essential problems that are as follows:                (a) Cu line thickness (trench depth) control and resistance control are unsatisfactory.        (b) The thermal expansion coefficient (CTE) of low-k dielectrics is high, and it causes final accidents during heat cycles.        (c) Ultra-low-k materials are not resistant to chemical mechanical polishing (CMP).        
To solve these problems, a hybrid-type insulating film has been proposed (e.g., see JP-T 2004-523910). However, most organic polymers used in such hybrid-type insulating films are poorly soluble in organic solvent and are problematic in that they may deposit in coating solutions and may form depositions in insulating films. These problems are serious in the art. To solve the problems, when the polymers are so modified that their main chain has a folded structure in order to have an increased solubility, then their glass transition point lowers and their heat resistance also lowers, and, after all, it is not easy to obtain polymers that satisfy both the intended properties and the solubility.